There are many problems extant with current state of the art suspension units, whether they be for bicycles, motorcycles, four-wheel vehicles, on or off road. The shock designer must constantly weigh the relative importance of handling, control and ride comfort, and decide which direction to compromise the suspension performance toward the vehicle's intended use. The only way to avoid these compromises would be to have a suspension that could anticipate every motion, and act to resist or comply instantaneously. While many attempts have been made at developing a computer controlled suspension that will do just that, none are able to achieve such a result. An object of the present invention is to reduce these compromises without requiring the use of a computer or electrical components.
In the past, springing means and methods have been the first in line for compromise during the process of specifying suspension components for a given vehicle. Too stiff a spring rate prevents the suspension from using enough travel to cope with bumps or surface irregularities, and transmits a harsh ride, as well as reduced cornering grip and traction under these conditions. Too soft a spring rate and the ride motions become excessive and weight transfer induces large shifts in the attitude of the chassis during braking and cornering. Excessive bottoming can also occur. This compromise has been further complicated in light vehicles such as motorcycles and bicycles, where rider weight is a relatively large percentage of the total sprung weight of the vehicle. For example, rider weight can be over 90% of total sprung weight in the case of a bicycle. With such a vehicle, a single spring rate will not be well suited for all rider weights. The skill level of the rider or operator of the vehicle is also a consideration when selecting a spring rate.
There is a need for an improved hydraulic suspension unit which provides a more flexible springing medium with more tuning capability, which can be adjusted without resorting to physically changing components. An object of the present invention is to provide such a hydraulic suspension unit.
Another compromise made with conventional shock absorbers is the amount of rebound damping. With conventional shock absorbers, there is always a damping effect present, even if this damping is undesirable. Too much rebound damping can cause harshness in the ride as the suspension skips off the tops of bumps rather than allowing the wheel to follow the surface into a depression. In a succession of bumps this can lead to loss of control as the wheel fails to return to full extension before hitting the next bump, meaning less available travel to negotiate the next bump, and more importantly, since the spring will be compressed whenever the shock is not at full extension, it will provide a higher force to resist the upward movement of the wheel upon hitting the next bump. This problem is usually described as "packing down". Too little rebound damping can cause an uncomfortable ride, by allowing too much upward movement of the vehicle after hitting bumps, or due to weight transfer in cornering, braking or accelerating. Too little rebound damping can also allow excessive cycling of the suspension after these inputs, as the spring's energy remains undamped, and is returned to the spring. Another problem is that too little rebound damping can cause the vehicle to launch skyward after large impacts, or when leaving the face of a jump. This launching effect is caused when the suspension reaches full compression, maximizing the stored energy in the spring, which is then returned at a high velocity, due to inadequate rebound damping.
There is a need for an improved hydraulic suspension unit which overcomes these drawbacks and disadvantages of the conventional suspension unit with respect to rebound damping. An object of the present invention is to provide an improved hydraulic suspension unit which solves these problems.
Compression damping is another area which has been compromised in the construction of conventional hydraulic suspension units. A vehicle with excessive compression damping will feel very responsive to control inputs, sometimes aiding handling by increasing control. This is usually at the expense of cornering grip or traction, as the wheel is unable to react quickly enough to even minor surface imperfections, much less bumps or major impacts and the contact pressure between the tire and terrain surface will be less consistent. When encountering a large bump, too much compression damping prevents the wheel from moving up over the bump quickly enough, thus translating impact to the chassis. Conversely, too little compression damping places too much reliance on the springing means for purposes of resisting excessive suspension compression due to weight transfer caused by cornering, braking, accelerating or bottoming forces. This can cause unwanted ride motions, as well as hard metal-to-metal impact on severe bottoming.
There is a need for an improved hydraulic suspension unit which addresses the conflicting requirements it is asked to fill with respect to compression damping. These include controlling the onset of initial ride motions, whether initiated by terrain changes or control inputs, and limiting the maximum velocity allowed in compression thus preventing harsh metal-to-metal bottoming. It is also desired that compression damping be accomplished while minimizing the transmission of bump impacts to the chassis. An object of the present invention is to provide an improved hydraulic suspension unit for a vehicle which addresses these conflicting requirements it is asked to fill.
These and other objects are attained by the improved hydraulic suspension unit for a vehicle of the present invention, the suspension unit comprising first and second members arranged in telescoping relation with one another for relative movement along a longitudinal axis of the suspension unit responsive to the relative motions between a vehicle wheel and the vehicle body compressing and extending the suspension unit. Means containing a hydraulic liquid are provided. The containing means include a first chamber containing hydraulic liquid in compressive force transmitting relation between the first and second members. The volume of the first chamber is decreased and increased with relative movement of the first and second members toward and away from one another along the longitudinal axis, respectively.
The containing means further includes a reservoir containing hydraulic liquid and passage means connecting the first chamber and the reservoir to permit the flow of hydraulic liquid between the first chamber and the reservoir. The reservoir includes a movable wall which can be moved back and forth to increase and decrease the volume of the reservoir as a function of the hydraulic liquid flowing to and from the reservoir, respectively.
The suspension unit further comprises spring means for resiliently biasing the movable wall against the hydraulic liquid in the reservoir with a force which is a function of the amount of movement of the spring means and in turn the position of the movable wall and volume of the reservoir. The spring means stores energy upon movement of the movable wall increasing the volume of the reservoir with the flow of hydraulic liquid to the reservoir. Stored energy is released by the spring means upon movement of the movable wall decreasing the volume of the reservoir with the flow of hydraulic liquid from the reservoir to the first chamber.
Compression damping means are provided for damping the flow of hydraulic liquid from the first chamber to the reservoir when the suspension unit is compressed to cause relative movement of the first and second members toward one another along the longitudinal axis decreasing the volume of the first chamber. Rebound damping means are also provided for damping the flow of hydraulic liquid to the first chamber resulting from the spring means releasing energy stored therein by moving the movable wall to decrease the volume of the reservoir and flow hydraulic liquid from the reservoir to the first chamber for extending the suspension unit. The rebound damping means allows relative movement of the first and second members away from one another for extending the suspension unit by external forces on the suspension unit without resistance from the rebound damping means while continuing to damp the flow of hydraulic liquid to the first chamber from the reservoir resulting from release of stored energy of the spring means. The rebound damping means includes a rebound damping valve which is movable in response to pressure of the hydraulic liquid thereon for opening and closing the passage means from the reservoir to the first chamber during release of stored energy from the spring means.
In order to provide a more flexible spring means with more tuning capability, the spring means of the suspension unit may be any combination of air, coil or elastomer springs, which can be separately adjusted for preload, providing maximum tuning flexibility without resorting to physically changing components. In a disclosed embodiment of the suspension unit, the spring means includes a pressurized gas arranged in an enclosed space in the suspension unit for acting on the movable wall of the reservoir. A coil spring acting on the movable wall can also be provided in the enclosed space containing the pressurized gas. Means are also provided for separately adjusting a preload or spring characteristic of each of the gas spring and the coil spring of the spring means.
A further feature of preferred embodiments of the suspension unit is that the passage means directs all of the flow of hydraulic liquid from the first chamber to the reservoir via the compression damping means and directs all of the flow of hydraulic liquid from the reservoir to the first chamber via the rebound damping means. Forcing 100% of the shock fluid displaced by extension or compression of the suspension unit through a single path, through the rebound damping means or through the compression damping means, allows more accurate and consistent damping control. The spring means is arranged to act directly on the movable wall of the reservoir, causing the fluid pressure to act on the cross-sectional area of the shock shaft forcing the shock to extend or resist compression. The movable wall may take the form of a reservoir piston, a resilient bladder or a flexible diaphragm. With this arrangement, the spring force and rebound damping have a direct relationship with each other that allows unique manipulation capabilities of their interaction.
By properly selecting the shaft/reservoir diameter ratio, the spring means, whether air, steel or elastomer, can have a mechanical advantage (or disadvantage) when acting on the shock shaft through the reservoir movable wall, allowing flexible packaging.
The maximum speed of expansion of the suspension unit due to release of stored energy from the spring means is controlled according to the invention by means for adjustably limiting the maximum flow area for hydraulic liquid flowing past the rebound damping valve from the reservoir to the first chamber when the rebound damping valve is open. This means for adjustably limiting the maximum flow area in a disclosed embodiment includes a mechanical stop limiting the opening extent of the rebound damping valve, and externally accessible means for adjusting the position of the stop.
Control of the hydraulic liquid pressure necessary for opening the rebound damping valve to permit the flow of hydraulic liquid from the reservoir to the first chamber and release of stored energy of the spring means is accomplished according to the invention by externally accessible means for adjustably, resiliently biasing the rebound damping valve in a closed position. In one form of the invention, the rebound damping valve is a poppet valve. The externally accessible means for adjustably, resilienting biasing includes a coil spring and means for adjusting a preload on the coil spring resiliently biasing the poppet valve in the closed position.
A performance characteristic of the hydraulic suspension unit of the present invention is that the rebound damping valve only affects the rebound velocity when such velocity is due to the force imparted by the spring means when it is returning stored energy after some initial compression. The magnitude of the stored energy can vary greatly and can be simply due to the force needed to support the static, sprung weight of the vehicle, or to the further compression of the suspension due to cornering, braking, bumps or other terrain variations. The extension, or rebound velocity of the shock is not effected or resisted by the shock absorber, if the rebound motion is due to external forces extending the shock or suspension. For example, if one end of the vehicle were to be lifted suddenly by skyhooks, the suspension unit of the present invention would not resist the immediate downward movement of the wheels as they come off the ground.
This effect allows the wheels to the extension limit of the suspension unit to follow small or large depressions in the surface of the terrain, maintaining traction and control, yet during any movement involving the return of stored energy from the spring, full rebound control is always attained. Suspension geometry can also cause forces to extend the shock absorber, as in certain anti-dive or anti-squat applications. These forces are also allowed to extend the suspension unit to its extension limit without the resistance of damping. The feature permitting external adjustment of the rebound damping characteristics makes the suspension unit of the invention particularly suited for use in lightweight vehicles such as bicycles and motorcycles where the rider weight is a relative large percentage of total sprung weight of the vehicle. However, the use of such a feature is not necessary to realize improved performance and the suspension unit of the invention is also useful in other vehicles.
A compression damping means in the disclosed embodiments includes a compression damping valve which is movable in response to pressure of the hydraulic liquid thereon for opening and closing the compression damping valve for controlling the flow of hydraulic liquid from the first chamber through the passage means to the reservoir during compression of the suspension unit. Means are also provided for adjustably biasing the compression damping valve in its closed position for controlling the hydraulic pressure and hence compressive force on the suspension unit necessary for opening the compression damping valve to permit the flow of hydraulic liquid from the first chamber through the passage means to the reservoir and the compression of the suspension unit. The compression damping valve is in the form of a flexible disc in the disclosed embodiments. The means for adjustably biasing applies an adjustable preload on the disc to affect the hydraulic pressure necessary to deflect the disc and open the compression damping valve.
The maximum speed of compression of the suspension unit is controlled by adjustably limiting the maximum flow area for hydraulic liquid flowing from the first chamber to the reservoir when the compression damping valve is open. An adjustment means for this purpose in a disclosed embodiment includes a mechanical stop limiting the opening extent of the compression damping valve, and externally accessible means for adjusting the position of the stop.
In one embodiment of the invention, the means for adjustably limiting the maximum flow area includes an additional valve located in the passage means upstream of the compression damping valve with respect to the flow of hydraulic liquid from the first chamber to the reservoir. Externally accessible means are provided for adjusting the extent which the additional valve restricts the flow of hydraulic liquid in the passage means during compression of the suspension unit. In the disclosed embodiment this additional valve is in the form of a needle valve. Thus, externally accessible means are provided for independently adjusting the amount of damping provided by each of the compression damping means and the rebound damping means.
Another feature of the invention is that each of the compression damping means and the rebound damping means of the hydraulic suspension unit acts as a check valve against the flow of hydraulic liquid in the opposite direction than that which is damped thereby. Further, the rebound damping valve is preferably arranged for movement so as to displace hydraulic liquid on the first chamber side of the rebound damping valve during opening of the valve. The volume of the rebound damping valve and its linear travel during opening are selected to provide displacement of a predetermined volume of hydraulic liquid and hence a predetermined expansion of the suspension unit during opening of the valve.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.